<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>发布订阅模式</title>
</head>
<body>
    <script>
        // 事件触发器
        class EventEmitter {
            constructor () {
                // { "click": [fn1, fn2], "change": [fn] }
                this.subs = Object.create(null) // 这个对象没有原型，提升性能，只用于存储键值对
            }

            // 注册事件
            $on (eventType, handler) {
                this.subs[eventType] = this.subs[eventType] || []
                this.subs[eventType].push(handler)
            }

            // 触发事件
            $emit (eventType) {
                if (this.subs[eventType]) {
                    this.subs[eventType].forEach(handler => {
                        handler()
                    })
                }
            }
        }

        // 测试
        let test = new EventEmitter()

        test.$on("click", () => {
            console.log("click1")
        })
        test.$on("click", () => {
            console.log("click2")
        })
        test.$emit("click")
    </script>
</body>
</html>